In conventional coking operations, when a charge of coke is ready to be pushed, a door at each end of the coke oven is removed, a ram-type pusher is positioned at one end of the oven, a coke guide is positioned at the other end, and an open hopper car is positioned at the discharge of the coke guide. The pusher expels the glowing coke cake through the coke guide, from which it falls into the open hopper car, which may be moving slowly transversely to the coke discharge in an effort to distribute the coke more or less evenly along the length of the hopper car. The hopper car is then quickly transported to a quenching station where the coke is drenched with large quantities of water to lower its temperature below the kindling temperature.
At least two separate phenomena relating to the yield of coke are associated with the pushing operation. First, the dropping of the coke as it is discharged from the oven and coke guide into the hopper car below breaks the semi-rigid cake of coke from its shape conforming to the interior of the oven into randomly sized lumps. Due to the nature of the blast furnace operation, chunks of coke smaller than a certain size are unacceptable. In the conventional process described above, however, a substantial portion of the coke degrades into unusable dust, known as "coke breeze", or into chunks smaller than the minimum acceptable size.
Secondly, the glowing coke, once exposed to the atmosphere, ignites and continues burning until the temperature of the coke is reduced to below its kindling temperature, as by quenching with large quantities of water. Depending on the relative locations of the coke oven and the quenching station, a portion of the coke can be consumed prior to its being quenched. In addition, the quenching operation itself causes the coke to break up, further degrading it.
Accordingly, with the cumulative losses of usable coke through breakage, through literally burning the coke away during the oven-to-quench station transport operation, and further degradation upon water quenching, the net coke output can be substantially less than the gross amount actually discharged from the oven.
Further disadvantages are associated with conventional coke oven operation with water quenching. For instance, the heating value of water-quenched coke is generally lower than coke which has undergone a so-called dry quench. Known dry quench systems, discussed below, typically employ an inert gas passed through the coke to absorb the sensible heat and, accordingly, do not involve the contact of water with the coke. The lower heating value of water-quenched coke stems from the residual moisture content of the coke which results despite attempts to meter the amount of quench water to supply only as much as will be evaporated during the quenching process. The difficulties in accurately metering the water result from such variables as the nonuniform application of the water to the coke, the uneven distribution of the coke within a hopper car, charge-to-charge variations in the coke yield, etc.
Additionally, with economy in energy consumption becoming increasingly important, employing the high heat content of a charge of coke to simply boil and evaporate away quench water is a relatively ineffective use of significant amounts of heat which might more effectively be utilized through a heat recovery system.
Considering a separate but related and important aspect of coking operations, such operations are notorious for the environmental pollution they generate. Conventional operations employing a water quench technique produce relatively high levels of pollution during the pushing and quenching operations described above.
During pushing, the cascading of the coke into the hopper cars creates considerable dust simply from the impact. Coupled with the continual emission of volatiles along with the smoke from the burning which occurs, and the particulate-laden steam generated from any on-site water spraying, considerable particulate matter is released to the atmosphere. Subsequently, in the water quenching operation, large quantities of particulate-laden steam are generated. The problem is even more acute where recycled cooling water, already having a high particulate content, is used.
In order to reduce the discharge of contaminants during pushing, hoods of various types ranging from those which enclose only the coke guide and the hopper car, or a portion of it, as it is positioned in front of a particular oven, to types which enclose the entire discharge side of the coke oven battery have been suggested to reduce the discharge of contaminants during the pushing operation. It will be appreciated that this latter approach involves high capital operating maintenance and repair costs. Insofar as the quenching operation is concerned, several hood and tower arrangements have also been suggested for use with the conventional process described of transporting the coke in hopper cars to a water quenching station.
Efforts to reduce the pulverization upon impact and/or to ameliorate the pollution resulting from the pushing and quenching operations have resulted in some coke handling techniques which depart from the conventional systems described above. For example, systems are known which involve pushing the coke cake into a perforate box which is then water quenched. Such an arrangement has the disadvantage of exposing at the glowing coke to the atmosphere and, of course, quenching water. Further modifications to systems employing perforate coke boxes described above include the placing of hoods over the coke boxes themselves to contain the emissions.
While some of the perforate coke box-type systems described offer some advantages over the conventional process described above, among the remaining disadvantages are the generation of pollutants (even though contained), inefficient dissipation of the sensible heat of the coke and the introduction of undesirable moisture content through water quenching.
Another alternative approach offering increased efficiency of the coking operation and pollution reduction is the dry quenching system mentioned above. In such a system, instead of quenching with water, an inert, i.e., oxygen-free, gas is passed through the coke. The sensible heat absorbed by the inert gas may then be recovered, as in boilers, with the inert gas being continuously cleaned and recycled. With such a system, high quality, dry coke is produced. British Pat. No. 183,113 (1923) discloses such a system. Some subsequently disclosed dry quench systems employ covered buckets to transport the coke from the point of coke oven discharge to a large blast furnace-type hopper to contain the coke while the inert gas is passed through it. While, as noted even in the British patent, the latter approach involves the double handling of the coke, it offers the advantage of reduced pollution during the transporting as well as the dry quenching operation.
Known dry quenching systems are subject to some offsetting disadvantages, however, including the pulverization problem discussed above and the often large capital expenditures required for a blast-furnace type of heat recovery system and/or for modifications required to retrofit existing coking operations.
An object of the present invention is to provide a system for receiving and cooling a charge from a coke oven which virtually eliminates the discharge of contaminents into the environment from the time the coke is pushed from the coke oven through the time the cooled coke is deposited for further processing and use, while at the same time increasing the quality and yield of the coke and facilitating the recovery of a significant portion of the sensible heat of the glowing coke. Even in instances where provision is not made to recover the heat, the initial stage of a slow cooling process provides further opportunity to cure the coke while at the same time permitting the removal of additional coke oven by-products.
A further object is to provide a system of the type described above and offering the advantages set forth which may be economically employed in both existing and newly constructed coking facilities.
A more specific object is to provide a system of the type described above which allows a large amount of coke to be undergoing various phases of cooling such that the heat exchange process may be efficiently carried to near equilibrium.
Yet another object is to provide a system as set forth above which may be adapted to a variety of dry quenching techniques.
Still another object is to provide a system of the above type which accommodates considerable latitude in the location of the cooling area relative to the coke oven battery.
These and other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings, in which: